Abstract text (incl. figure legends and references)

Developing low-cost and efficient oxygen evolution electrocatalysts is key to decarbonization. A novel, facile, surfactant-free and gram-level biomass-assisted fast heating and cooling synthesis method is reported for synthesizing a series of carbon-encapsulated dense and uniform FeNi nanoalloys with a single-phase face-centered cubic solid-solution crystalline structure. This method also enables precise control of both size and composition. Atomic resolution scanning transmission electron microscopy (STEM) images show uniform nanoparticles with a narrow size distribution of sub-5 nm. STEM analysis also demonstrates a single-phase face-centered cubic solid-solution crystalline structure, in good agreement with XRD pattern analysis. STEM mapping and line-scan analysis show that FeNi nanoalloy experiences surface restructuring under the OER condition and turns into alloy-core/oxides shell structure. Electrochemical measurements show that among FexNi(1−x) nanoalloys, Fe0.5Ni0.5 has the best performance. DFT calculations support the experimental findings and reveal that the optimally positioned d-band center of O-covered Fe0.5Ni0.5 renders a half-filled anti-bonding state, resulting in moderate binding energies of key reaction intermediates. By increasing the total metal content from 25 to 60 wt%, the 60% Fe0.5Ni0.5/40% C shows an extraordinarily low overpotential of 219 mV at 10 mA cm-2 with a small Tafel slope of 23.2 mV dec-1 for OER, which are much lower than most other FeNi-based electrocatalysts and even the state-of-the-art RuO2. It also shows robust durability in an alkaline environment for at least 50 h. The gram-level fast heating and cooling synthesis method is extendable to a wide range of binary, ternary, quaternary nanoalloys, as well as quinary and denary high-entropy-alloy nanoparticles. [1]

[1] Y. Wang, W. Nong, N. Gong, T. Salim, M. Luo, T. L. Tan, K. Hippalgaonkar, Z. Liu, Y. Huang, Small 2022, 18, 2203340.